1. Field of the Invention
One aspect of this invention relates to the production of hydrocarbons from subterranean formations. In another aspect, the invention concerns a method of recovering free gas from naturally-occurring gas hydrate deposits. In a further aspect, the invention involves a process of sequestering greenhouse gases in subterranean formations.
2. Description of the Prior Art
Gas hydrates are crystalline solids composed of gas molecules surrounded by cages of water molecules. These gas molecules are usually light hydrocarbons (C1–C4). Gas hydrates form a solid phase above and below the pressure and temperature conditions required to form ice. Gas hydrates historically have been considered a nuisance in the oil industry because of their spontaneous formation in oil and gas pipelines, which would hamper the flow of oil within the pipeline.
However, naturally-occurring gas hydrate deposits have become the focus of attention in recent years as an alternative fuel source for the energy industry. Large, naturally-occurring gas hydrate deposits are found near many existing oil deposits, along with non-traditional reservoirs found in permafrost and shallow buried sediments in deep-sea environments. Some sources estimate that in the United States alone, the amount of methane contained within natural methane hydrate deposits is 200 times the amount existing as free methane in natural gas deposits. Furthermore, the amount of potential energy in natural gas hydrate deposits is estimated to be twice that of the currently existing oil, coal, and natural gas deposits combined.
Conventional methods of natural gas extraction from gas hydrates involve heating and/or depressurizing the gas hydrates in order to release the natural gas. However, there are two major problems with these conventional methods. First, they require a large amount of energy to be added to the system, resulting in a high cost of extraction. Second, they destabilize hydrate formations because both depressurization and heating cause the hydrate to melt. This can lead to the destabilization and/or collapse of sediments that contain hydrates and other nearby subterranean formations. Because gas hydrates are usually extracted near oil and natural gas deposits, such instability can result in problems with the extraction of oil and natural gas.
An existing problem, unrelated to the extraction of gas hydrates, concerns the release of greenhouse gases into the Earth's atmosphere. A variety of current industrial processes produce excess greenhouse gases, especially carbon dioxide, that may contribute to the catastrophic climate changes if continually released into the atmosphere. However, disposal of the excess greenhouse gases in a manner that permanently prevents release of the gases can be quite expensive. Thus, it would be desirable to provide a new method of sequestering greenhouse gases, such as carbon dioxide, that is more effective and economical than previous disposal methods.